JPH08131777A - Exhaust gas treatment method - Google Patents

Abstract

PURPOSE: To provide an exhaust gas treatment method which does not require a large-scale inactive gas generator and a nitrogen storage tank, which are necessary for a conventional exhaust gas treatment method for treating exhaust gas containing SO2 , and is advantageous in costs. CONSTITUTION: Exhaust gas containing at least SOx, directly or after the injection of ammonia, is introduced into a reactor 3 which is a filling bed for a carbonaceous catalyst 4 to be subjected to desulfurization or desulfurization- denitration. Next, the carbonaceous catalyst 4 deactivated by contacting exhaust gas is introduced into a regenerator 7 to be regenerated by heating. SOx in the desorption gas generated during the regeneration by heating is absorbed and removed by the aqueous solution or slurry of an alkali agent in a SOx absorption column 19, and the obtained SOx-removed desorption gas, directly or after being dehumidified by a dehumidifier 20, is used in an exhaust gas treatment plant as inactive gas for seal gas, heating purge gas, carrier gas, emergency gas, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for desulfurization or desulfurization / denitration treatment of exhaust gas containing at least SO _X with a carbonaceous catalyst. In particular, the desorbed gas generated during the regeneration treatment of the carbonaceous catalyst is an inert gas. And a method used in an exhaust gas treatment plant.

[0002]

BACKGROUND ART SO _X or boiler exhaust gas containing the SO _X and NO _X,, sintering furnace exhaust gas, the incinerator waste gas, etc., such as dust, after mixing of directly or ammonia, downward carbonaceous catalyst from above It is well known to treat exhaust gas by passing it through a moving bed reactor which is packed so as to move. In this method, SO _X in the exhaust gas is adsorbed on the carbonaceous catalyst as sulfuric acid and removed. Further, when ammonia is injected into the exhaust gas, SO _X is adsorbed and removed as an ammonium salt thereof in addition to sulfuric acid, and NO _X is reduced to harmless nitrogen.

Upon contact with exhaust gas, sulfuric acid and ammonium salts such as acidic ammonium sulfate and ammonium sulfate are gradually accumulated in the carbonaceous catalyst, and the desulfurization activity and denitration activity of the carbonaceous catalyst decrease with time, so that the carbonaceous catalyst is regenerated. There is a need. The carbonaceous catalyst whose activity has temporarily decreased is conveyed to the top of the moving bed type regenerator and is supplied to the inside of the regenerator through a supply valve. In the process of moving to the lower part in the regenerator, it is heated to about 300 to 600 ° C. and regenerated. Since the carbonaceous catalyst is oxidized and consumed by oxygen, the regeneration treatment is performed in an oxygen-free inert gas atmosphere.

In this regeneration treatment, a large amount of SO ₂ , N ₂ , CO ₂ and H ₂ O is generated by the decomposition of sulfuric acid and its ammonium salt adsorbed on the carbonaceous catalyst, so that it is inevitable in the regenerator. Although an inert gas atmosphere is used, an inert gas may be positively supplied as a carrier gas in order to quickly desorb the adsorbed substance on the surface of the carbonaceous catalyst. The carbonaceous catalyst thus heated and regenerated is cooled, discharged from the bottom of the regenerator, supplied again to the top of the reactor, and reused.

On the other hand, in the conventional exhaust gas treatment method, a moving bed type is also used as the regenerator for continuously treating the exhaust gas. Therefore, in this type of regenerator, the catalyst supply section at the top and the catalyst feeding section at the bottom are used. In order to prevent leakage of high-concentration SO ₂ gas from the valve provided in the discharge part and to prevent corrosion of the low temperature part above and below the regenerator, apart from the carrier gas, nitrogen, CO _2, etc. Inert gas is supplied as a seal gas and a purge gas. Of the seal gas and the purge gas, the inert gas that has entered the regenerator is SO
_{2 It} also plays the role of a carrier gas that promotes desorption of gas.

Conventionally, these carrier gas, seal gas,
As a method of supplying the inert gas used for the purpose of the purge gas, a method of supplying nitrogen gas from a large liquid nitrogen cylinder or an air separation device (a pressure swing for separating oxygen and nitrogen in the air) in the exhaust gas treatment plant. Device or a cryogenic separation device) is installed to supply nitrogen gas, and air is passed through a packed bed of coal, coke, etc.
_A method of using an inert gas generating furnace that is converted to ₂ or a method of obtaining an inert gas by burning in a furnace such as heavy oil / light oil has been adopted.

In the above exhaust gas treatment method, a method of using a moving bed reactor (adsorber) filled with a carbonaceous catalyst (adsorbent) such as activated carbon, activated coke, activated char, etc. does not lower the exhaust gas temperature, It has many advantages over the wet method, such as the small amount used. Moreover, the carbonaceous catalyst which has become inactive due to the adsorption treatment has an advantage that it can be easily regenerated by simple heating regeneration.

[0008]

However, in the method of using liquid nitrogen as the inert gas used in the conventional exhaust gas treatment plant, nitrogen is expensive, and it is necessary to carry it in frequently. In the method of supplying the inert gas, there is a problem that a special inert gas generating equipment is required.

Further, in the conventional exhaust gas treatment method, the high concentration S generated inside the catalyst supply section and the discharge section of the regenerator is used.
Since an inert gas such as N ₂ was supplied from the outside in order to prevent leakage of O ₂ gas to the outside and to prevent corrosion of the low temperature parts of the upper and lower parts of the regenerator, and depending on the case, the adsorbed substance Since the carrier gas was supplied for the purpose of desorbing quickly, it was necessary to install an inert gas production facility in the exhaust gas treatment plant or prepare a large amount of liquid nitrogen or the like.

Therefore, in order to solve this problem, the present invention does not need to prepare special inert gas generating equipment or a large amount of liquid nitrogen, etc., and produces an inert gas using exhaust gas in an exhaust gas treatment plant. It is an object of the present invention to provide an exhaust gas treatment method that is used.

[0011]

In order to solve the above-mentioned problems, the exhaust gas treatment method of the present invention uses at least SO.
Exhaust gas containing _X , directly or after injecting ammonia,
In a method for treating exhaust gas by an exhaust gas treatment plant in which a carbonaceous catalyst is introduced into a packed bed for desulfurization or desulfurization / denitration treatment, and then the carbonaceous catalyst inactivated by contact with the exhaust gas is heated and regenerated, (1) inactivation The SO _x in the desorbed gas generated during the heating and regeneration of the carbonaceous catalyst is absorbed and removed with an aqueous solution or slurry of an alkali absorbent, and (2) the obtained S
The desorbed gas from which O _X has been removed is directly or after being dehumidified and then used as an inert gas in the exhaust gas treatment plant.

The alkali absorbent used in the exhaust gas treatment method of the present invention contains calcium-containing minerals such as sodium hydroxide, calcium carbonate, calcium hydroxide, calcium oxide, magnesium hydroxide, limestone and dolomite, or calcium. The fluid combustion ash can be selected from one kind or two or more kinds.

In the exhaust gas treatment method of the present invention, the desorbed gas from which SO _X has been removed is dehumidified by pressurizing and cooling, or
Alternatively, the carbonaceous catalyst discharged from the regenerator can be used as an adsorbent for removing water.

The desorbed gas from which SO _X and water have been removed in the exhaust gas treatment method of the present invention is one or more selected from the seal gas in the exhaust gas plant, the heating purge gas, the carrier gas and the emergency gas. It can be used as an inert gas for applications.

The exhaust gas treatment method of the present invention will be described based on the example of the exhaust gas treatment plant shown in FIGS. 1, 2 and 3. FIG. 1 shows an example of the overall configuration of an exhaust gas treatment plant used in the exhaust gas treatment method of the present invention. Exhaust gas at about 60 to 180 ° C. is introduced into the cross-flow moving bed reactor 3 through the exhaust gas introduction line 1. At this time, when the desulfurization activity of the carbonaceous catalyst is to be improved, or when denitration is performed simultaneously with desulfurization, ammonia is simultaneously injected into the exhaust gas introduction line 1 via the ammonia addition line 2. The exhaust gas is desulfurized and denitrated while contacting the carbonaceous catalyst 4 that descends in the reactor 3, and then discharged from the reactor 3 to the outside through a clean gas discharge line 5.

In the reactor 3, the carbonaceous catalyst 4, which has been inactivated by adsorbing sulfuric acid, ammonium sulfate and the like by contact with exhaust gas, is withdrawn from the bottom of the reactor 3, and a moving bed type regenerator 7 is passed through the catalyst transfer line 6. Is brought to the top of
It is supplied into the regenerator 7 through the supply valve V ₁ . The carbonaceous catalyst 4 is stored in the regenerator 7 under an inert gas atmosphere at 30
It is heated to 0 to 600 ° C and regenerated. For this heating, the heating gas is introduced from the heating gas introduction line 8 into the heating chamber 15 in which a large number of catalyst transfer pipes 16 provided in the middle portion of the regenerator 7 are arranged, and the carbonaceous catalyst 4 is exchanged by heat. The heated gas that has been heated and then heat-exchanged is discharged from the heated gas discharge line 9.

In order to prevent the high concentration SO ₂ gas from leaking out from the top supply valve V ₁ and the bottom discharge valve V ₂ of the regenerator 7, and in the cooler section 10 above and below the regenerator 7. To prevent corrosion, an inert gas is introduced as a seal gas and / or a purge gas from the seal gas introduction lines 22 and 23 and the purge gas introduction lines 11 and 12. In some cases, an inert gas is introduced as a carrier gas through the carrier gas introduction line 13. In the regenerator 7 of FIG. 1, the desorbed gas is taken out from the desorbed gas line 14 above the regenerator 7,
It is also possible to stop introducing the carrier gas from the carrier gas introducing line 13 and change the desorbed gas to be taken out from the carrier gas introducing line 13.

The carbonaceous catalyst 4 heated and regenerated in the heating chamber 15 of the regenerator 7 is cooled in the cooler section 10 below the regenerator 7,
It is discharged through the discharge valve V _{2 at the} bottom of the regenerator 7. Then, it is passed through a separator 17 such as a vibrating screen to remove the powdered carbonaceous catalyst 4 and dust, and is returned to the top of the reactor 3 by a catalyst transfer line 18 such as a conveyor.

High-concentration SO _X gas generated in the regenerator 7 (mostly SO ₂ and some SO ₃ in some cases)
The desorbed gas containing oxygen is passed through the desorbed gas line 14 to SO _X.
It is supplied to the absorption tower 19. SO _X present in desorbed gas
Is removed by a wet SO _X absorption tower 19 that circulates an aqueous solution or slurry of an alkaline agent. A spray type is shown as an example for the SO _X absorption column 19 in FIG. 1, but any of the filling type, the bubbling type, the perforated plate type and the like may be used for the SO _X absorption column of other types. Also, if you install them in two or more stages in the series,
The SO _X absorption performance can be improved.

As the alkali agent usable in the SO _X absorption tower 19, calcium such as sodium hydroxide, calcium carbonate, calcium hydroxide, calcium oxide, magnesium hydroxide, limestone, dolomite, a magnesium-containing mineral, or calcium is used. A fluidized combustion ash containing is used. The liquid that has absorbed SO _X in the SO _X absorption tower 19 is sent to a process for recovering gypsum, magnesium sulfate, etc. after being neutralized and oxidized.

Since the inert gas discharged from the wet SO _X absorption tower 19 contains a large amount of water, it is preferable to dehumidify it when it is used as a seal gas, a purge gas or a carrier gas for the regenerator 7. Therefore, a part or all of the inert gas from the SO _X absorption tower 19 is supplied to the dehumidifier 20 and dehumidified. As a method for dehumidifying the inert gas from the SO _X absorption tower 19, a normal dehumidifier 20 for applying pressure and cooling is used.
(Compressor and chiller combination) can be used. After the inert gas from the SO _X absorption tower 19 is dehumidified, it is used as a seal gas, a purge gas, and a carrier gas used in the exhaust gas treatment plant of the present invention through the treated gas supply line 21, and the remaining gas. Is returned to the exhaust gas introduction line 1 at the inlet of the reactor 3 or the clean gas discharge line 5 at the outlet.

Further, a part of the inert gas from the SO _X absorption tower 19 can be used as an emergency gas when abnormal heat generation of the carbonaceous catalyst 4 occurs in the reactor 3 and other exhaust gas treatment plants. it can. When the inert gas is used for such a purpose, there is no problem even if the inert gas before dehumidification is used.

As a method of dehumidifying the inert gas from the SO _X absorption tower 19 different from the above, FIG. 2 shows a flow chart of dehumidification treatment using a carbonaceous catalyst regenerated from the regenerator 7 as a dehumidifying material. As shown in FIG. 2, part or all of the carbonaceous catalyst discharged from the regenerator 7 is introduced into the dehumidifier 20 (countercurrent or crossflow type moving bed moisture adsorption tower), while the regenerator 7 An inert gas containing water obtained by treating the desorbed gas discharged from the SO _X absorption tower 19 into the dehumidifier 20 can be dehumidified. In this method, the regenerator 7
Since the carbonaceous catalyst discharged further has almost completely removed water, the water can be efficiently adsorbed.

The carbonaceous catalyst used in the dehumidifier 20 is sent to a separator 17 for removing dust and catalyst powder, and then returned to the top of the reactor by a catalyst transfer line 18 and is recycled. In the flow chart of the carbonaceous catalyst of the method of FIG. 2, the separator 17 can be arranged upstream of the dehumidifier 20 as shown in FIG.

Calcium chloride, silica gel, zeokite, etc. can be used as the adsorbent for removing moisture for the dehumidifier used in the present invention, but when these adsorbents are used, it is necessary to purchase a new one. In addition, a regenerator for regenerating those adsorbents is required, but when using a carbonaceous catalyst, it is sufficient to use the one in the exhaust gas treatment plant. Therefore, it is convenient because regeneration only for recovering the water adsorption activity is unnecessary. If a large amount of ammonia is present in the inert gas that has been dehumidified by the above method, pass the inert gas through a device partially filled with a carbonaceous catalyst in which sulfuric acid from the reactor is adsorbed. Thus, ammonia can be removed.

[0026]

The exhaust gas containing SO _X and NO _X is passed through a moving bed reactor packed with a carbonaceous catalyst (usually, a counter-current type or a cross-flow type is used to continuously treat the exhaust gas). In the exhaust gas treatment method of treating, SO _X is adsorbed and removed as sulfuric acid on the surface of the carbonaceous catalyst. When ammonia is added to the exhaust gas and treated through a packed bed of carbonaceous catalyst, SO _X is adsorbed and removed as ammonium salts such as sulfuric acid and acidic ammonium sulfate / ammonium sulfate, while NO _X is decomposed into nitrogen. . Since sulfuric acid and its ammonium salt are adsorbed on the surface of the carbonaceous catalyst upon contact with the exhaust gas, the carbonaceous catalyst is temporarily poisoned and inactivated. Therefore, the inactivated carbonaceous catalyst is continuously discharged from the reactor and supplied to a moving bed type regenerator for heating and regeneration. Heat regeneration in the regenerator is carried out under an inert gas (or reducing gas) atmosphere (supplying an inert carrier gas or in an exhaust gas treatment plant without using a carrier gas to prevent the carbonaceous catalyst from being consumed by oxygen. In the generated inert gas atmosphere), about 300-6
It is carried out at a temperature of 00 ° C. At this time, the sulfuric acid and its ammonium salt adsorbed on the carbonaceous catalyst are decomposed by the reactions of the following formulas (1) to (5).

[0027]

[Equation 1] That is, the sulfuric acid and ammonium salt adsorbed on the surface of the carbonaceous catalyst are dissociated by the reaction formulas (1) to (3), and then SO ₂ , N ₂ are decomposed by the reaction formulas (4) and (5).
Is converted to. After all, the desorbed gases are SO ₂ , N ₂ , C
It becomes a mixed gas of O ₂ and H ₂ O. When the amount of injected ammonia in the reactor is large, or depending on the structure of the moving bed regenerator, a small amount of ammonia may be contained in the desorbed gas (usually several to several thousand ppm). Means for Solving the Problem] can be removed by the method described in the section.

The SO _X concentration in the desorbed gas varies greatly depending on the amount of the inert carrier gas, the operating conditions of the apparatus, etc., but is usually several% to several tens%. In any case, the inside of the regenerator is extremely toxic and is in a corrosive gas atmosphere,
The use of inert seal gas and purge gas can prevent the leakage of SO _X gas to the outside and prevent the corrosion due to the condensation of SO _X gas in the lower and upper low temperature parts of the regenerator. . Further, by supplying an inert carrier gas into the regenerator as necessary, smooth desorption of SO _X is promoted.

Further, in an exhaust gas treatment plant using a carbonaceous catalyst, there is a possibility that heat generation due to the reaction of carbon and oxygen can occur in many places, and in particular, the reactor is filled with a large amount of carbonaceous catalyst. Therefore, a problem such as partial heat generation (generation of hot spots) may occur. By preparing an inert emergency gas obtained from the desorbed gas, when such a problem occurs, this gas can be supplied to extinguish the fire.

[0030] As the present invention can be seen from the above reaction formulas (1) to (5), from simple _{CO 2, N 2, H 2} O by removing the SO _X in the desorbed gas with an alkaline agent Inert gas can be obtained. Further, by dehumidifying this inert gas, a better inert gas composed of CO ₂ and N ₂ can be obtained. These gases can be used for each of the above applications in the exhaust gas treatment plant of the present invention.

[0031]

EXAMPLE A carbonaceous catalyst (S) discharged from a moving bed reactor in a desulfurization / denitration plant for treating coal-fired boiler exhaust gas of 10,000 Nm ³ / hour shown in FIG.
O ₄ ^2- adsorption amount, 75 mg / g carbonaceous catalyst, NH ₄ ⁺ adsorption amount, 7 mg / g carbonaceous catalyst) to a moving bed regenerator 222
It was fed at kg / h and regenerated at about 430 ° C. 1. Nitrogen gas is supplied as a seal gas from the seal gas introduction lines 22 and 23 at 0.5 Nm ³ / hour, respectively, and nitrogen gas is used as a purge gas from the purge gas introduction lines 11 and 12.
It was supplied at 5 Nm ³ / hour. Nitrogen gas as a carrier gas was not newly supplied because these gases serve as a carrier gas. At this time, the desorption gas line 1
The composition of the desorbed gas discharged from No. 4 was SO ₂ : 18.6.
_{%, CO 2: 3.7%,} H 2 O: 42.2%, NH 3:
0.002%, HCl: 1.4%, HF: 0.7%, N
₂ : 33.4%. In addition, each gas concentration is a wet standard display.

This desorbed gas was taken out at 1 Nm ³ / hour,
A production test of an inert gas was conducted. A desorbed gas of 1 Nm ³ / hr was bubbled from the bottom of the SO _X absorption tower 19 filled with a calcium carbonate slurry having an inner diameter of 5 cm and a water depth of 1 m at 50 ° C. using a diffuser. This time,
A slurry liquid containing 20% of calcium carbonate was supplied from another lower portion of the SO _X absorption tower 19 at a rate of 5 liters / hour. The overflowed used slurry was recovered as gypsum after neutralization and oxidation treatment.

When the inert gas obtained from the top of the SO _X absorption tower 19 was analyzed, SO ₂ : 0.002%, C
_{O 2: 9.0%, H 2} O: 12.2%, NH 3: 0.0
02%, N ₂ : 78.8%, and HCl and HF were not detected. In addition, pressurize this gas to 7 atm.
When it was cooled to ℃ and dehumidified, CO ₂ : 10.2.
%, N ₂ : 89.7%, H ₂ O: 0.1%, SO ₂ ,
NH ₃ was detected. From this example, it is understood that the inert gas obtained by the method of the present invention can be sufficiently applied as the inert gas required in the exhaust gas treatment plant.

[0034]

According to the method of the present invention, by utilizing the gas in the exhaust gas treatment plant to produce an inert gas, it is possible to utilize the inert gas, the conventional exhaust gas containing SO ₂ There is no need to prepare a large-scale inert gas generator or a nitrogen storage tank as in the exhaust gas treatment method for treating hydrogen, and there is a merit in cost.

[Brief description of drawings]

FIG. 1 shows an example of the overall configuration of an exhaust gas treatment plant used in an exhaust gas treatment method of the present invention.

FIG. 2 is a flow chart of a regeneration treatment and a dehumidification treatment of a deactivated carbonaceous catalyst from a reactor.

FIG. 2 is another flow diagram of a regeneration treatment and a dehumidification treatment of the deactivated carbonaceous catalyst from the reactor.

[Explanation of symbols]

1 Exhaust gas introduction line 2 Ammonia addition line 3 Reactor 4 Carbonaceous catalyst 5 Clean gas discharge line 6,18 Catalyst transfer line 7 Regenerator 8 Heating gas introduction line 9 Heating gas discharge line 10 Cooler part 11, 12 Purge gas introduction line 13 Carrier Gas introduction line 14 Desorption gas line 15 Heating chamber 16 Catalyst transfer pipe 17 Separator 19 SO _X absorption tower 20 Dehumidifier 21 Treated gas supply line 22, 23 Seal gas introduction line

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[Procedure amendment]

[Submission date] February 16, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 shows an example of the overall configuration of an exhaust gas treatment plant used in an exhaust gas treatment method of the present invention.

FIG. 2 is a flow chart of a regeneration treatment and a dehumidification treatment of a deactivated carbonaceous catalyst from a reactor.

FIG. 3 is another flow chart of the regeneration treatment and dehumidification treatment of the deactivated carbonaceous catalyst from the reactor.

[Explanation of Codes] 1 Exhaust gas introduction line 2 Ammonia addition line 3 Reactor 4 Carbonaceous catalyst 5 Clean gas discharge line 6,18 Catalyst transfer line 7 Regenerator 8 Heating gas introduction line 9 Heating gas discharge line 10 Cooler section 11, 12 Purge gas introduction line 13 Carrier gas introduction line 14 Desorption gas line 15 Heating chamber 16 Catalyst transfer pipe 17 Separator 19 SO _x absorption tower 20 Dehumidifier 21 Treated gas supply line 22, 23 Seal gas introduction line

Claims (4)

[Claims] 1. Exhaust gas containing at least SO _X is introduced directly or after injecting ammonia into a packed bed of carbonaceous catalyst for desulfurization or desulfurization / denitration treatment, and then carbon inactivated by contact with the exhaust gas. In a method for treating exhaust gas by an exhaust gas treatment plant for heating and regenerating a high-quality catalyst, (1) SO _X in desorbed gas generated during heating and regeneration of an inactivated carbonaceous catalyst is absorbed and removed with an aqueous solution or slurry of an alkaline absorbent. (2) An exhaust gas treatment method, wherein the obtained desorbed gas from which SO _X has been removed is used as an inert gas in the exhaust gas treatment plant directly or after dehumidifying. 2. One of fluid combustion ash in which the alkali absorbent contains calcium or a mineral containing calcium such as sodium hydroxide, calcium carbonate, calcium hydroxide, calcium oxide, magnesium hydroxide, limestone, dolomite, or the like, or The exhaust gas treatment method according to claim 1, wherein the exhaust gas treatment method is selected from two or more kinds. 3. Dehumidification of the desorbed gas from which the SO _X has been removed is performed by pressurizing and cooling, or by using the carbonaceous catalyst discharged from the regenerator as an adsorbent for removing water. The exhaust gas treatment method according to claim 1 or 2, characterized in that. 4. The method of using the desorbed gas as an inert gas is a method of using one or more kinds selected from a seal gas in an exhaust gas treatment plant, a heating purge gas, a carrier gas, and an emergency gas. The exhaust gas treatment method according to claim 1, wherein the exhaust gas treatment method is used as an active gas.